It is not an exaggeration to say that the miniaturization of semiconductor integrated circuits has been achieved as a result of developments in photolithography and associated technologies. As is widely known, these photolithography developments are supported by what can be broadly classified as two technologies. One is the exposure wavelength and numerical aperture of the reduction projection exposure apparatus known as a stepper or scanner, and the other is the resist characteristics, and mainly the transferred resolution of a photoresist composition generated by transferring a mask pattern using the above reduction projection exposure apparatus. A combination of these technologies has brought significant improvements in the precision of the processing of semiconductor integrated circuit patterns by photolithography.
The light source used in the reduction projection exposure apparatus has continued to shift towards shorter wavelengths in order to meet the demands for higher resolution circuit patterns. Typically, for a resist resolution of 0.5 μm, a mercury lamp for which the main spectrum is the 436 nm g-line is used, for a resolution of approximately 0.5 to 0.30 μm, a mercury lamp for which the main spectrum is the 365 nm i-line is used, for a resolution of approximately 0.3 to 0.15 μm, 248 nm KrF excimer laser light is used, and for resolutions of 0.15 μm or less, 193 nm ArF excimer laser light is used, and in order to achieve even greater miniaturization, 157 nm F2 excimer laser light, 126 nm Ar2 excimer laser light and EUV (extreme ultraviolet radiation: wavelength 13 nm) are also being investigated.
On the other hand, in the case of photoresist compositions, combinations with organic and inorganic antireflective films and innovations within the illumination systems are now commonplace, and in the case of lithography using KrF excimer laser light, photoresist compositions that will enable prolonged life for KrF photoresists are being developed, including photoresist compositions that target resolutions of approximately 110 nm, which represents no more than λ/2. Furthermore, in the case of lithography using ArF excimer lasers, favorable ArF photoresist compositions that will enable future mass production of fine patterns with a 90 nm node or smaller are now being sought. Moreover, lithography using the aforementioned F2 excimer lasers is now attracting considerable attention as a technology that will take a pivotal role in the processing of future ultra fine patterns of 65 nm or smaller, and considerable development is now being pursued of photoresist compositions that can be favorably applied to microfabrication using such F2 excimer laser lithography.
Obtaining the types of fine patterns described above using conventional positive photoresist compositions that include an alkali-soluble novolak resin and a quinonediazide group-containing compound as the main components is extremely difficult, and the development of resists that use shorter wavelength radiation, including far ultraviolet light (200 to 300 nm), excimer lasers such as KrF or ArF lasers, electron beams or X-rays, is now keenly sought. One type of resist that is attracting considerable attention as a resist capable of achieving high levels of resolution, capable of utilizing a catalytic reaction and chain reaction caused by acid generated upon irradiation to produce a quantum yield of 1 or greater, and also capable of achieving high sensitivity is a chemically amplified resist, and development of these resists is flourishing.
Resists for use with short wavelength light sources such as KrF excimer lasers or ArF excimer lasers require a high level of resolution capable of reproducing a pattern of very fine dimensions, as well as high sensitivity to this type of short wavelength light source. One example of a known resist capable of satisfying these requirements is a chemically amplified positive resist composition which includes a base resin that exhibits increased alkali solubility under the action of acid, and an acid generator that generates acid on exposure.
Chemically amplified positive resist compositions that have been proposed as ideal resist materials for exposure methods using a KrF excimer laser typically employ a polyhydroxystyrene-based resin in which a portion of the hydroxyl groups have been protected with acid dissociable, dissolution inhibiting groups as the base resin (for example, see patent reference 1). Examples of the most commonly used acid dissociable, dissolution inhibiting groups include so-called acetal groups, such as chain-like ether groups typified by a 1-ethoxyethyl group and cyclic ether groups typified by a tetrahydropyranyl group, as well as tertiary alkyl groups such as a tert-butyl group or 2-alkyl-2-adamantyl group, and tertiary alkoxycarbonyl groups typified by a tert-butoxycarbonyl group.
Furthermore, chemically amplified positive resist compositions that have been proposed as ideal resist materials for exposure methods using an ArF excimer laser typically employ, as the base resin, a (meth)acrylate-based resin in which a portion of the hydroxyl groups have been protected with the same type of acid dissociable, dissolution inhibiting groups as those described above. Of these, resins that use a tertiary alkyl group as the acid dissociable, dissolution inhibiting group are particularly widely used (for example, see patent reference 2).
As disclosed in the non-patent references (3 to 5) listed below, examples of the above chemically amplified resists include fluoroalcohols containing an acetal group, a tertiary alkyl group such as a tert-butyl group, a tert-butoxycarbonyl group or a tert-butoxycarbonylmethyl group as the acid dissociable, dissolution inhibiting group.
[Patent Reference 1]
Japanese Unexamined Patent Application, First Publication No. Hei 04-211258
[Patent Reference 2]
Japanese Patent (Granted) Publication No. 2,881,969
[Non-Patent Reference 3]
T. Hagiwara, S. Irie, T. Itani, Y. Kawaguchi, O. Yokokoji, and S. Kodama, J. Photopolym. Sci. Technol., Vol. 16, p. 557, 2003
[Non-Patent Reference 4]
F. Houlihan, A. Romano, D. Rentkiewicz, R. Sakamuri, R. R. Dammel, W. Conley, G. Rich, D. Miller, L. Rhodes, J. McDaniels and C. Chang, J. Photopolym. Sci. Technol., Vol. 16, p. 581, 2003
[Non-Patent Reference 5]
Y. Kawaguchi, J. Irie, S. Kodama, S. Okada, Y. Takabe, I. Kaneko, O. Yokokoji, S. Ishikawa, S. Irie, T. Hagiwara and T. Itani, Proc. SPIE, Vol. 5039, p. 43, 2003.